ZIP4 Is a Novel Cancer Stem Cell Marker in High-Grade Serous Ovarian Cancer

SIMPLE SUMMARY: Ovarian cancer is the most deadly gynecologic cancer. The treatment options for ovarian cancer, and for the recurrent cancer in particular, are limited. One of the major obstacles is the presence of drug-resistant cancer stem cells. The aim of this study is to identify and characterize a new cancer stem marker, namely ZIP4. ZIP4 is a transporter for human essential element zinc. Our results have shown that ZIP4 is not only a novel and potent stem cell marker, but also a target for developing innovative treatment for ovarian cancer. In addition, ZIP4 is interacting with another oncogene, NOTCH3. Both ZIP4 and NOTCH3 play important roles in tumor development in ovarian cancer. This interaction may represent a useful target for ovarian cancer treatment. ABSTRACT: High-grade serous ovarian cancer (HGSOC) is one of the most deadly and heterogenic cancers. We have recently shown that ZIP4 (gene name SLC39A4), a zinc transporter, is functionally involved in cancer stem cell (CSC)-related cellular activities in HGSOC. Here, we identified ZIP4 as a novel CSC marker in HGSOC. Fluorescence-activated cell sorter (FACS)-sorted ZIP4(+), but not ZIP4(−) cells, formed spheroids and displayed self-renewing and differentiation abilities. Over-expression of ZIP4 conferred drug resistance properties in vitro. ZIP4(+), but not ZIP4(−) cells, formed tumors/ascites in vivo. We conducted limiting dilution experiments and showed that 100–200 ZIP4(+) cells from both PE04 and PEA2 cells formed larger tumors than those from 100–200 ALDH(+) cells in mice. Mechanistically, we found that ZIP4 was an upstream regulator of another CSC-marker, NOTCH3, in HGSOC cells. NOTCH3 was functionally involved in spheroid formation in vitro and tumorigenesis in vivo in HGSOC. Genetic compensation studies showed that NOTCH3, but not NOTCH1, was a critical downstream mediator of ZIP4. Furthermore, NOTCH3, but not NOTCH1, physically bound to ZIP4. Collectively, our data suggest that ZIP4 is a novel CSC marker and the new ZIP4-NOTCH3 axis represents important therapeutic targets in HGSOC.